The invention relates to apparatus for and methods of testing for leaks in flexible packages containing loosely packaged product and some air.
The packages with which the invention is concerned are for example potato crisp packs in the form of a sealed bag having two opposite rectangular faces, the bag containing the potato crisps and also some air which tends to prevent undue collapse of the bag. Other kinds of products are packages in similar bags and as will be evident, the invention could also be applied to packages for other products.
In the packaging of potato crisps, there is some tendency to produce some packages which have an unacceptably large air leak, possibly by being inefficiently sealed or completely unclosed. These sub-standard packages tend to occur at random amongst satisfactory packages and if the packaging apparatus has to be stopped every time a sub-standard package is detected, the output of the packaging apparatus is reduced. It is also disadvantageous to fail to detect sub-standard packages because these can eventually lead to customer complaints.
It has already been proposed in our published UK Patent Application No. 2138150-A to provide apparatus for testing for leaks in such a package in which a plurality of probes engage against one face of the package under the influence of gravity at successive probing stations. This action tends to expel air from a leaky package. At the last of these stations, a measure of the thickness of the package is obtained by obtaining a measure of the position of certain probes. This measured information indicates whether or not there is a leak in a package.
With our earlier proposal, it is necessary for each kind of package with which the apparatus may be used to establish in advance an appropriate thickness for determining whether a package is or is not satisfactory. With packaging apparatus of this kind, it is often desirable to change over from one size of package to another or from one packaged product to another and it is desirable to be able to do this with a minimum of adjustments in the packaging equipment. For these reasons it would be desirable to provide a bag testing apparatus in which it is not necessary to re-set the measure of a satisfactory package when changing from one kind of package to another.